In particular in the automotive sector, components having micromechanical sensor elements are often used for detecting various physical quantities (pressure, temperature, air mass, acceleration, revolution speed). Typically, measuring elements on diaphragms disposed above a cavity are often utilized for this purpose. For the production of the diaphragm and the cavity, apart from so-called surface micromachining, in which stacks of layers made up of sacrificial layers and functional layers are deposited, patterned and selectively removed, so-called bulk micromachining is known as well, in which patterns are worked out of solid material.
From EP 1 043 770 A1, a method is discussed in which at least one trench is initially produced in a substrate using a first etching step. After passivation of the walls of the trench, the cavity is formed in the course of a second anisotropic etching step. Enlargement of the cavity can be carried out in a third etching step, which is also anisotropic, by removing the walls between a plurality of adjacent trenches.
In DE 102 00 40 433 56 A1, which is assigned to Bosch GmbH, to whom the present application is also assigned or under an obligation of assignment, and which is not prior art as to the present application, it is discussed how a buried cavity is produced with the aid of a single trench etching process. The trench etching process has a first trench etching step, which creates a depression. In the course of this first trench etching step, the etching step is implemented in two phases. In a first phase, an indentation is initially produced in alternation, whose walls are covered by a passivation agent in the second phase. Repetition of the two phases therefore produces the depression. The cavity is subsequently produced in the second trench etching step, the depression serving as access hole to the cavity. This is done by implementing the etching process of the first phase for a considerably longer period of time in the second trenching step, without a passivation taking place. By repeating the steps of this trench etching process, a plurality of caverns lying underneath the other is able to be produced in the substrate.
From EP 1441 561 A2, another method is known in which recesses or caverns disposed underneath one another are able to be produced. To this end, different layers are first deposited on a substrate. Using a masking metal layer, depressions are made in the deposited layer sequence. The depression is made with the aid of an anisotropic dry etching method. Starting from the depressions, cavities, which are interconnected underneath the deposited layers, are produced in the substrate by means of a subsequent isotropic etching process or by plasma etching. In another step, an opening in the substrate can be produced from the rear of the substrate. The two cavities may then be interconnected via an additional anisotropic etching process.